The effects of a low fat, high carbohydrate diet on serum and breast ductal fluid hormones and lipids will be studied in healthy premenopausal women (25-45 years old). After following a 30% AHA diet for 1 month, subjects will be instructed to follow a 10% fat, high carbohydrate diet for 2 months. All meals will be provided to ensure maximum dietary compliance. Estradiol, LH, FSH, progesterone, estrone, and estrone sulfate will be measured in blood samples collected at regular intervals.